Conventionally, as an apparatus for cooling an electronic device installed outdoors, an air conditioner or a heat exchanger has been used. They provide the advantage of completely intercepting the open air before it can reach air inside the device, and the benefit of cooling the inside of the device with clean air. However, they have the disadvantage that they require power to drive an air conditioner. Furthermore, there exists a cooling apparatus for introducing open air in the device by using a filter as a filtering member. However, there is a problem with the apparatus in that the filter removes only dust and takes in the outside moisture directly into the device, thus corroding circuit components and the like that are mounted within the apparatus.
One of the prior arts that prevents dew condensation by reducing humidity within an electronic device is disclosed in Japanese patent literature JP-A-4-294597.
FIG. 1 shows a conventional cooling apparatus for electronic device described in the abovementioned patent literature. The conventional apparatus is connected to an electronic device and cools the inside of the electronic device to reduce humidity within the device by using a cooling fan.
As shown in FIG. 1, cooling apparatus for electronic device 32 comprises moisture absorption duct 34 at an air intake side of a body of the apparatus that cools heat generated by components within electronic device 31, absorption duct 34 being filled with reversible moisture absorbent 35 having a reversible characteristic for discharging absorbed moisture at a temperature above a predetermined temperature. Channel switching duct 36, blockage plate 37, and cooling fan 33 are provided at an air exhaust side of moisture absorption duct 34. Blockage plate 37 is designed to open and close synchronously with the turning on and off of a power source of electronic device 31.
When the power source of electronic device 31 is turned on, blockage plate 37 is opened and thus exhaust air channel L is opened, causing hot air due to the heat generated by the components in electronic device 31 to be attracted by the rotation of cooling fan 33. At this time, reversible moisture absorbent 35 is dried and regenerated at the temperature above the predetermined temperature. When the power source is turned off, exhaust air channel L is blocked by blockage plate 37, preventing the open air from entering electronic device 31, and causing reversible moisture absorbent 35 that has been regenerated and activated to absorb moisture from the residual air in the device. This results in the prevention of dew condensation in electronic device 31.
Despite the configuration wherein humidity within the electronic device is reduced to prevent dew condensation, the aforementioned conventional apparatus presents a problem that, since it utilizes the reversible moisture absorbent that is dried and regenerated at a temperature above the predetermined temperature, when the temperature within the electronic device does not exceed the predetermined temperature due to cooling, the reversible moisture absorbent cannot be dried and regenerated, and thus humidity increases. The repeated turning on and off of the power source for drying and regenerating the reversible moisture absorbent, this involving the most important operation for the device, causes a problem in the operability of the device, and necessitates frequent open/close operation of the blockage plate.